This invention relates to a sheet sorter which is provided with a plurality of trays and adapted to sort sheets by switching trays for receiving sheets, and also to a copier, a printer or like image forming apparatus provided with such a sheet sorter.
There has been conventionally known a copier for reading a document image and forming a plurality of copy images. Such a copier is provided with a sheet sorter including a plurality of trays on which sheets are placed in order to sort a specified number of sheets having the same image formed thereon for each set. In recent years, the sheet sorter has also been used to sort sheets having images formed thereon for each user or each personal computer or for each personal computer job in a copier commonly used by a plurality of users or in a printer connected with a plurality of personal computers.
The users and the personal computers might designate or not the trays on which the sheets are to be placed. When the tray is designated, the sheet is placed on this tray. On the other hand, when no tray is designated, the sheet is placed on the tray specified beforehand. This specified tray is generally the one on which a maximum number of sheets can be placed. Accordingly, the users know on which trays their sheets are to be placed.
A new sheet having an image formed thereon is discharged onto the sheet already placed on the tray. Thus, even in the case that a plurality of users designate the same tray or designate no tray to place sheets of a plurality of users on the same tray, if each user quickly take the sheet(s) out of the tray after the image formation, there is a low possibility of mixing his sheet(s) with the sheet(s) of the others. Therefore, the sheet(s) of each user can be easily distinguished.
However, the users do not necessarily take the sheets out quickly after the image formation, i.e., they may take time to take the sheets out. If the sheets are taken out after a while, the sheets of many users may be placed one over another. In such a case, each user is likely to experience an incapability of easily finding his own sheet(s) although he knows on which tray his sheets are placed. The tray is often undesignated when the sheets are to be taken out after a while. In such a case, it is more difficult to find the own sheets out since the sheets are placed on the tray on which a maximum number of sheets can be placed.